Art of effecting heat exchange



'Sept. 29, 1931. w. D. LA MONT ET AL 1,825,321

ART OF EFFECTING HEAT EXCHANGE Original Filed Oct. 7, 1926 2 Sheets-SheeT 1 INVE TORS M/ALTER D. AMozvr ALFRED f. ERNST BY wui-rspmom,

ATTORNEY Sept. 29, 1931. w. D. LA MONT ET AL ART OF EFFECTING I IEAT EXCHANGE Original Filed Oct. '7, 1926 2 Sheets-Sheer. 2

IIIIIIIIIIIIIIIIIII/IIIIIII/IIIII/IIIIIII/lII/IIIIIII ZIIIIIIIIIIIIIIIIIIIIII/IIIIIII/IllIl/III/IIIIIIIII/I! INVENTORS WALTE D. LAMONT ALFRED ATTORNEY l atented Sept; 29 1931 UNITED STATES PATENT OFFICE WALTER DOUGLAS LA MONT, OF COLEBROOK, CONNECTICUT, AND ALFRED F. ERNST, OF RUTHERFORD, NEW JERSEY, ASSIGNORS TO LA MONT CORPORATION, OF NEW YORK,

N. Y., A CORPORATION OF NEW YORK ART OF EFFECTIN G HEAT EXCHANGE Original application filed'October 7, 1926, Serial No. 140,099; Divided and this application filed November 4, 1930. Serial No. 493,258.

This invention in its broadest aspects relates to the exchange of heat between substances, the temperatures of which are different, with the object either of increasing the heat content of one substance, or decreasing that of the other, and a general object of the invention is so to direct and control this heat exchange in accordance with the physical laws of heat and the physical characteristics of the different substances between which the exchange is to take place as to obtain substantially the practicable maxi-v mum of efliciency of heat transfer, or in other words so to direct and control this heat exchange that within the limits of practicability substantially a maximum of heat transfer will take place from one substance to another during the time that the substances are in heat-exchanging relation to -,2 each other and that the rate of heat transfer will likewise be increased.

\ Although the invention is herein particularly illustrated v in its application to the transfer of heat from heated gases tovapors,

it will be understood that the invention is not restricted in its utility or applicability to the uses or to the embodiments herein illustrated and described, but that it has quite general utility in the heat exchange art.

It is well known that the transfer of heat from one substance to another or throughout a particular substance takes place by conduction, by convection or by radiation, or by one or more or all of these modes of transfer. The present invention, while intended to take advantage of the exchange of heat by conduction and by radiation, at leastv to the same extent as by the methods and with the apparatus heretofore employed, relates particularly to the transfer of heat somewhat after the manner that heat transfer is accomplished by convection, an object of the in,- vention being to utilize convection, or bodily translation relative. to the stream movement 1 of theparticles (not molecules) of at least one of the substances to or from which heat is to be transferred, in such manner and un der such control as to determineto a substantial degree the speed, direction and amplitude of the heat-transferring movements taining the practicable maximum of heatand contacts of the particles of the heatconveying vehicle or fluid and thereby obtain substantially the practicable maximum of heat-transferring efficiency while the heat-conveying vehicle and the substance to or from which heat is to be transferred remain in heat-exchanging proximity to each other.

The invention relates particularly to obexchanging eificiency when the heat convey- 0 ing vehicle is a fluid. When a fluid, whether liquid or gas, it is used as the heat conveying vehicle, it will be apparent that in order to insure as great heat transfer as possible between the fluid and the substance to be heated or cooled, as many contacts as possible of different particles of the fluid with the substance to be heated or cooled must be effected, since conduction from the heated particles of the fluid to the particles of the fluid which are not heated is comparatively little, particularly if the fluid be a gas An important object of the present 1nven tion, therefore, is so to control the move 7 ment of a heat conveying fluid in heat-exchanging relation to the substance to be heated or cooled as to insure, while in such heat-exchanging relation, the maxlmum of heat transferring contacts.

Leaving out of account for the moment' any movement of the substances to be heated or cooled, the invention aims, in the first place, to move the vehicle from or to which heat is to be transferred, whether gas or liquid, at such a velocity with relation to the substance to be heated or cooled, and also in such relation to the exposed surface of such substance, that advantage may be taken of the phenomenon which occurs when a fluid is moved at a velocity appreciably higher than that which produces uniform rectilinear, motion of the particles (not molecules) of the fluid. This velocity at which a change from rectilinear motion of 05 the particles of the moving fluid occurs has commonly been called the critical velocity of the fluid. It is the velocity which is obtained by laboratory methods in experiments to determinethat speed of flow at which a 100 particle of fluid deviates from its rectilinear motion.

The present invention takes advantage of this critical velocity of fluids by so controlling the velocity of the fluid utilized to'effect the heat transfer, whether to or from this fluid, that its velocity will be at or above the critical velocity of this fluid, thereby producing an appreciable motion of the particles of the fluid in directions at angles to the direction of flow of the fluid.

The invention aims further so as to control this velocity that, where desirable, substantially the maximum displacement of the particles of the fluid laterally with respect to the direction of flow may be obtained. Such a velocity may, for convenience, be termed maximum ranging velocity where the term ranging is used to define the lateral movements of the particles with respect to the direction of flow of the fluid.

4 In addition to controlling the velocity of the fluid used for heat transfer, whether to or from this fluid, so as to obtain an effective ranging movement of the particles of the fluid, for the purposes in view, whether or not this be the velocity producing the maximum ranging motion, the invention further aims to concentrate, within the crosssection of the flow of the fluid moving at the desired ranging velocity, a plurality of portions of the substance to be heated or cooled, or the heat-exchanging surface, in such way that the heat-exchanging surface has its area extended principally in the direction of the flow of the fluid, and that it has its several portions so spaced that these portions are within the field of the lateral ranging motion of the particles of the fluid, thereby to present to the ranging particles of the fluid as great an opportunity as possible for contact of such particles of the fluid with the substance to be heated or cooled, or the heat-exchanging surface. In other Words, an important object of the invention is so to subdivide the substance to be heated or cooled, or the heat-exchanging surface, that the distances apart and the locations of its respective portions will be within the limits of the ranging actionof the particles of the fluid, and preferably so to arrange these portions that there will be a heat-exchanging surface within the range of any particle no matter what the transverse direction of its ranging movement.

Not only is it important, for ultimate economy and efiicienoy, to provide heatexchanging or contacting surfaces within the range of movement of the particles of the heat conveying, fluid and so to determine the velocity of the fluid as to obtain the desired effective ranging movement, but it 18 also important that these heat-exchangmg surfaces be extendedalong the path of .movement of the heat conveying fluid a sufiicient distance to insure the desired total heat transfer. By so confining the fluid stream as to obtain an initial velocity of the heat conveying fluid approximating its maximum effective ranging velocity and also simultaneously so determining such a spacing of the different portions of the heatexchanging surface within the stream that the distance from any one portion to each of several adjacent portions will not be greater than the limits of the ranging action of the particles of the fluid, it will be seen that the desired or substantially the maximum amount of heat per unit of length of travel of the fluid or per unit of time will be transferred, since the opportunity for the molecules of the particles of the fluid to transmit their vibratory motion to the substance to be heated or to the heat-exchanging surface Will be substantially a maximum. It will further be seen that by extending the heat-exchanging surface along the path of travel of the heating fluid the desired total transfer of heat may be effected.

To effect such desired total transfer most efficiently, however, that is, with a minimum of apparatus and within a minimum of time, involves other considerations than mere extent of the heating surface along the path of travel of the fluid, even when such heating surface '.is so sub-divided at the point Where the heating fluid first comes into contact with it as to insure the desired exposure of the surface to the ranging action of the particles of the fluid at that point. As a result of the transfer of the heat of the heat conveying fluid to the heat-exchanging surface or the transfer of heat to the fluid, there is a cooling or heating of the fluid which effects a change in its density and therefore in the volume of the same weight of the moving fluid. When the fluid is employed as a heating fluid, if the spacing of the heat-exchanging surfaces throughout the path of travel of the fluid over said surfaces remains the same and provides the same cross-sectional area of the stream, not only will the increase in density due to cooling, with the resultant reduction in volume, affect the velocity of the fluid over the heat-exchanging surfaces in the later parts of its path of travel, but such reduction in volume and velocity will, within certain limits,- also (affect a reduction in the ranging motion of the particles of the fluid, and thus, with uniform spacing of the heating surfaces throughout the path of travel of the heating fluid thereover, in most cases reduce the contacts and the rate of heat exchange in the later parts of the path of travel.

A further important object of the present invention, therefore, is so to vary the spacing of the surfaces which confine and delib termiii'e the velocity of. the fluid stream that an effective ranging velocity may be maintained substantially throughout the travel of the fluid over such surfaces and so to space the heat-exchanging surfaces that each will be Within the ranging-action of the particles of the fluid throughout the travel of the fluid thereover. In the case of a heating fluid, therefore, both the stream confining and the heat-exchanging surfaces will preferably gradually approach each other along the latter parts of the path of movement of the fluid thereover, such narrowing of the distances between the different portions of the heat-exchanging surfaces being preferably so determined that, while avoiding excessive. draft loss, an effective ranging velocity of the fluid will nevertheless be maintained throughout its travel over the heat-exchanging surfaces and that these surfaces will be so located within the limits of the ran ing motion produced by the velocity at eac point along the path oftravel of the fluid that an eflicient heatexchanging bombardment of the surfaces by the particles of the fluid will take place throughout such travel.

It will be understood, of course, that other factors than the mere confining of the fluid stream so as to obtain and maintain a maximum ranging velocity enter into the obtaining of the practicable maximum of efli ciency of heat transfer. As above suggested, with uniform spacing of the heat-exchanging surfaces and a constant cross-sectional area of the fluid stream, reduction in volume due to loss of heat eflects both a reduction in velocity and a reduction in ranging movement of the particles of the fluids. If, however, the spacing of the surfaces which confine and which are located in the fluid stream be so reduced as to compensate for this reduction in volume and thus maintain a velocity which will maintain the maxi-mum ranging motion, it is probable that, in some cases, the additional power required to force the fluid between the closely'spaced surfaces would more than offset the increased efficiency of heat exchange, particularly where the heat exchange is being eflected for the urposes of power production. It will thus e seen that there is an advantage in the outer reaches of the pathof the fluid travel in effecting a compromise between that spacing of the stream confining surfaces w ich would produce the maximum ranging velocity of the gases and a spacing which, while not causing a marked draft loss, would, nevertheless, with the-reduced velocity produced by such spacing, be so great as to effect a marked reduction in the number of heat-exchanging contacts owing to the lowerin of the ranging action due to the lowere velocity. By the expression 6 effective ranging velocity is'therefore to be understood that velocity which, having regard to the spacing of the stream-confining and heat-exchanging surfaces required to produce it and having regard .to the draft loss and therefore additional power required with such a spacing as wouldmaintain the maximum ranging velocity nevertheless effects an acceleration of heat exchange (by reason of the marked increase in the heatexchanging V contacts between the surfaces and the particles of the fluid) over a velocity produced by a spacing of the steamconfining and heat-exchanging surfaces which while avoiding excessive draft loss, would, nevertheless reduce the velocity so much that the heat-exchanging surfaces would be spaced beyond the normal amplitude of ranging movement of the particles of the fluid for that velocit In other words, the invention aims to maintain an effective ranging velocity of the heat-conveying fluid by so restricting, at successive points along its path of flow, the cross-sectional area of the fluid stream flowing over the heat-exchanging surfaces distributed throughout the stream, and so spacing these heat-exchanging surfaces from each other in the stream that while the pitch and amplitude of the ranging action of the particles of the fluid resulting from the stream velocity produced by the restricted cross-sectional area is such as to insure an effective number of contacts of the particles of the heating fluid with the heatexchanging surfaces for the particular spacing of the heat-exchanging surfaces, nevertheless the resistance offered by the streamconfining "'and heat-exchangin surfaces to the flow of the fluid will not e such as to ,cause an excessive draft loss or uneconomically to impede the fluid flow.

Other objects and important features of the inventionwill appear from the following description and claims when considered in connection with the accompanying drawings, in which i Fig. 1 is a diagrammatic section illu'strat-' ing the shape of a fluid confining passage required to maintain a maximum ranging velocity of flow of the fluid therethrough under conditions in which the fluid either takes up or gives ofi' heat,-the diagram illustrating the shape of such a fluid passage when the rate of heat transfer follows the law of heat differential and the flow-impelling pressure is substantially uniform. vThis figure also illustrates in dotted lines the normal amplitude and pitch of the ranging motion of a particle of the fluid at this constant velocity; i

Fig. 2 is a view similar to Fig. 1, showing the possible actual path of travel of the ranging particle owing-to the fact. that the normal amplitude of its ranging motion produced by the uniform velocity is greater than the width of the passage required to produce the velocity W ereby the particle strikes the side wall of the passage before completing its lateral swing;

Fig. 3 is a view illustrating a modified shaping of the fluid passage, which while not suited to the maintenance of a uniform velocity of the fluid through the passage, nevertheless will maintain at all times such a velocity that the ranging motion produced thereby will have an amplitude and pitch suited to the dimensions of the passage;

Fig. 4 is a diagrammatic illustration of the possible practicable boundaries of effective ranging velocities;

Fig. 5 is a somewhat diagrammatic view illustrating the application of the invention to fluid passages on both sides of the heatexchanging surfaces of a heat exchange apparatus;

Fig. 6 is a section on the line 6-6 of Fig. 5;

Fig. 7 is a section on the line 77 of Fig. 5; and

Fig. 8 is a sectional view showing a modification of the transverse dimensions of the fluid passages by which passages of different shape but having the same hydraulic mean depth as those shown in Fig. 5 may be obtained.

As hereinabove suggested, the invention is directed to taking advantage of certain phenomena resulting from the movement of fluids through passages at velocities beyond those at whichthe particles of the fluid maintain a substantially rectilinear direction of movement, by so confining the fluid to or from which heat is to be transferred that the velocity of the fluid thus confined and subjected to its flow-impelling pressure will produce an effective ranging action of the particles of the fluid, and so exposing I the heat-exchanging surface to the fluid that there will be a portion of the surface within the range of substantially every particle of the fluid at substantially every point along the path of flow of the fluid thereover.

If we assume that the heat-conveying vehicle is a vapor or gas and that as it travels over the heat-exchanging surface it loses or takes up heat at a rate determined by its drop or rise in heat head at. different points along the path of travel, we then have a curve of reduction or increase in volume such as shown in Fig. 1 of the drawings. In this figure the curved lines 2 and 4 may be considered to represent, insection, the boundary walls of a passage for a heat conveying gas, these walls also providing heatexchanging surfaces. The reduction in the cross-sectional area of the passage toward the right in Fig. 1 corresponds to the reduction in volume of a gashaving a temperature drop varying in rate with its loss of heat head as it moves to the right along this passage. It will thus be seen that ifthere is a constant flow-impelling pressure on the gas the velocity of the gas will remain substantially uniform as it travels through the passage.

Leaving out of consideration any variation in the amplitude of the lateral ranging movement of the particle of the gas which might result from an increase in the density thereof, it will be apparent that if this constant velocity of the gas flowing through the passage bounded by the walls 2 and 4 is the maximum ranging velocity of the gas and that if at the point where the gas enters the passage the walls 2 and 4 are so spaced that a particle of gas followin the dotted line path 6 would, as it struc the wall 2, be substantially at the extremity of its movement to one side of the center of its line of motion; in other words, if the walls 2 and 4 at this point are spaced a distance apart equal substantially to the amplitude of the ranging motion of the particles of the gas at the maximum ranging velocity, then, with the maintenance of this velocity throughout the travel of the as through the passa e, this particle woul still tend to follow t e sinuous dotted path of movement shown in Fig. 1. Because of the confining walls, however, it would not be able to follow this path and 1t is quite probable that its path of movement would be more nearly like that of the solid line 8 in Fig. 2.

It will thus be seen that by so spacing the heat exchanging surfaces as to form a gas passage that will maintain the maximum ranging velocity of the gas throughout its travel over the heat-exchanging surfaces we obtain in the outer reaches of the travel of the gas a spacing of these surfaces closer than required for effective contact of the particles of the gas therewith. Moreover, with the relatively long gas passages essential for substantial total heat transfer, that is, substantial reduction of the heat head to zero, it is probable in most cases that the reduction in the cross-sectional area of the passage necessary to maintain the maximum ranging velocity for the outer reaches of the travel of the heating gas would be such as.

seriously to interfere 'with the draft. In other words, the draft loss of the increased frictional resistance to the movement of the gases would be so great that the additional power required to overcome this draft loss might more than offset the increased efliciency of heat exchange, particularly if the purpose of the heat exchange be the production of power.

One of the objects of the present invention, therefore, is so to shape the fluid passages that the fluid in traveling over the heat-exchanging surfaces, while not necessarily having its maximum ranging velocity at all points throughout its path of travel,

stream, or of the heat-exchanging surfaces within a thudstream, is therefore such that will yet maintain a velocity somewhat lower than the initial velocity, which will nevertheless produce an effective ranging motion of the particles of the fluid, a substantially limiting condition being that shown in Fig. 3, in which the sinuous path of travel of a particle of the fluid is shown as having its lateral limits substantially at the walls of.

the tube throughout its travel, such result being obtained by so shaping the passage that the velocity of fluid travel produced thereby as the fluid loses heat and volume, will cause a gradual reduction in the pitch and in the amplitude of the ranging motion at successive points along its path whereby the amplitude at each point is substantially equivalent to the transverse dimension of the passage at that point.

It will be apparent, as illustrated in Fig.

4 4, that the fluid velocity producing the ideal condition of ranging motion 1s not necessarily the maximum velocity obtainable, although from experiments heretofore conducted it has been ascertained that heat transfer within certain limits is dependent upon the velocity of movement of the heatconveying fluid over the heat-transferring surface. From an examination of Fig. 4, however, it will be seen that above the critical velocity there will be a velocity that will give the maximum amplitude of ranging motion, this being illustrated by the sinuous path a of the movement of a particle of the fluid at this velocity. It will further be apparent that as the velocity increases beyond this maximum ranging velocity the pitch will be greater but the amplitude less and that therefore within a confined passage of definite dimensions the number of contacts of the particles with the heat-exchanging surface will be less. This is shown by the sinuous line 'b'of the path of travel of the particle at a velocity above the maximum ranging velocity.

locity, both the pitch and the amplitude of the maximum ranging velocity. as shown by the sinuous hnec 1n Fig; 4. The'ideal spacmg of the surfaces which confine'the fluid when the fluid stream is moving at its max- With a velocity somewhat below the maximum ranging ve-' imum ranging velocity these surfaces will be spaced apart distances at or slightly within the amplitude of ranging motion of the particles of the fluid at that velocity. By this condition may be obtained substantially the maximum of surface contact and therefore of heat transfer.

s above pointed out, however, if we so arrange the heat-exchanging surfaces that they shape a passage for a heat-conveying gas which will maintain the initial maximum ranging velocity of the gas throughout its travel through the passage, we then meet the condition'illustrated in Fig. 1, in which the heat-exchanging surfaces are so spaced apart as not to obtain the maximum benefit of the amplitude of ranging motion pro-v duced by this maximum ranging velocity.

Moreover, with relatively long gas passages, the choking action in the outer reaches of the gas travel due to the restriction of the passage necessary to maintain the maximum ranging velocity might require the application of artificial draft-producing means, utilizing an amount of power more than equal to the increased efliciency of heat exchange resulting from this maintenance of the initial maximum ranging velocity through those parts of the gas passage.

It will be understood that there are two surface factors entering into the efliciency of heat exchange, one being the stream confining factor and the other the heat-exchanging factor. It will be apparent that in a relatively large gas passage the confining function may be effected by having the surfaces so located as to secure the desired velocity of stream flow without their necessarily being so located as heat-exchanging surfaces that they are within the amplitude of the ranging motion of the particles of the fluid produced by that velocity. It is therefore important not only so to locate the surfaces for confining the stream that they will produce the desired ranging velocity, but'also so to distribute the surfaces for heat-exchanging purposes throughout this stream that a portion of these surfaces will be within the range of motion of substantially every particle ofthe fluid at substantially every point along its path of travel. This. in the case of a heating fluid transferring its heat to the heat-exchanging surfaces. involves not only a restriction of the fluid passage to maintain aneflective ranging velocity, as the fluid loses heat in exchanging surface located within the limits of'the range of movement of substantially every particle at substantially every POlIlt along the path of travel. W

As above suggested in connection wlth the discussion of Figs. 1 to 3, in the practical application of the invention, for example, to the passagesfor heat-conveying gases between heat-exchanging surfaces, a compromise between a shaping of the gas passage and a location of the heat-exchanging surfaces therein such that the maximum ranging velocity of the gases would theoretically be maintained, that is, a proportioning of the gas passages to the variation in volume or in density of the heating gas with a resultant amplitude of ranging motion of the particles of the gas above that which can be efficiently utilized in the narrowed gas passage, on the one hand, and the maintenance of a uniform gas passage with the resultant lowering of the velocity of travel of the gas in the outer reaches of its travel and its attendant reduction of the ranging motion of the particles of the gas below an eflicient heat-exchanging level, on the other hand, and a compromise presents the best interrelationship of the heat-exchanging and fluid passage defining surfaces for eflicient and economical heat exchange. Such a compromise is illustrated diagrammatically in Fig. 3 in which the shaping of the heat-conveying gas passage has been so chosen that while it will not maintain the initial ranging velocity of the gas, whether maximum or otherwise, as the gas loses heat it neverthe less will maintain an effective ranging velocity. Moreover it avoids excessive draft loss and presents the heat-exchanging surfaces at all points within the limits of the ranging motion of the particles of the gas produced by the velocities at the respective points.

In revious attempts to solve the problem of e cient heat exchange, particularly in steam generating apparatus, alleged relationships between hydraulic mean depth and length of gas travel have been worked out. A comparison of the applications of such formulae to tubes of different diameters will show that such formulae do not take into consideration the equally important factor of turbulence or ranging. motion of the particles of the gas at given velocities and that a heat-exchanging structure answering the terms of such formulae might be constructed in which the efficiency of heat exchange would be very much less than that in which provision is made in the spacing of the heatcxchanging surfaces for utilizing to its fullest practicable extent the factor of turbulence or ranging motion.

As hereinabove suggested, the spacing of the heat-exchanging surfaces and the shaping of the gas passage illustrated in Fig. 3 is substantiall the limiting relationship of the surfaces or efiicient heat exchange, a wider spacin of the surfaces with the resultant lowering of the velocity of the gases probably producing an amplitude of ranging motion too low to insure effective contact of the particles of the gas with the heat-exchanging surfaces. The ideal spacing of the heat-exchanging surfaces and shaping of the gas passages to meet the average conditions is probably somewhat between that illustrated in Fig. 3 and that illustrated in Fig. 1, such a spacing making provision for utilization of a possible kinetic energy factor present in the higher ranging velocities. It is substantially such an intermediate shaping of the gas passages and spacing of the heat-exchanging surfaces that is illustrated and described as being embodied in a steam generator of the LaMont type in my copending application Serial No. 140,099 filed October 7, 1926 of which this present application is a division.

It will be noted that in said application for Letters Patent in which is shown the embodiment of the invention and embodiment of means for carrying out the novel process of the present invention in connection with steam generators, the mean hydraulic depth where the gases enter the gas passage to contact with the generating tube is comparatively low and is a mean hydraulic depth in every sense of the term. In other words, the tubes are so distributed through the heat chamber that the cross-sectional area of the gases surrounding each tube is substantially the same. Moreover, the mean hydraulic depth at the outlet end of the gas passage is still lower and the tubes here, as at the entrance end and at all points along their length, are so distributed throughout the cross-sectional area of the heat chamber that the cross-sectional area of the gases surrounding each tube is substantially the same.

In the disclosure of said copending application is given a figure and a calculation to support it illustrating the amount of heating surface to be placed in the gas space of a heat exchanger for the effective heat exchange described above. Such a degree of concentration of the heating surface per cubic foot of total volume of the gas passage, ,namely of the degree of 12 sq. ft. of heating surface per cubic foot of volume of the passage, is applicable to the present invention.

In Fig. 5, we have illustrated, in a somewhat diagrammatic view, the application of the invention to fluid passages on both sides of the heat-exchanging surfaces of a heating apparatus. Assuming that the fluids between which exchange of heat is to take place are both in the form of vapors or gases and that they are moving in counter-flow relation to each other, it will be obvious that the invention may be to advantage employed in the determination of the spacing of the heat exchange walls or surfaces and the shaping of the fluid pas- .vention, depth, reduced at the outlet end, but the sages on both sides of these walls or surfaces whereby, with the counter-flow arrangement illustrated in Fig. 5 and in cross section in Figs. 6 and 7, we would have a shaping and arrangement of the passages there shown in which the rising heating gases in the passagesg and the descending vapors to be heated in the passages 1; move between heat-exchanging walls or surfaces which shape passages for the gases that become restricted as the gases lose their heat to the vapors and also shape passagesfor the vapors that become enlarged to accommodate the increased volumes of the vapors as they take up heat from the gases. These passages, like those shown in Fig. 1, may approximate a shaping that would give substantially the maximum ranging velocity to the particles of, the respective vapors and gases and maintain this throughout their relative movement past each other, or they may conform more nearly to the preferred and more eflicient shaping of the passages in order to obtain an approximation of the l gath of travel of the particles shown in i 3. Fig. 5 also illustrates the possibility of an arrangement of the fluid passages in heat? exchanging apparatus so as to insure a substantially equal distribution of the heatconveying fluids over the heat-exchanging surfaces whereby the actual mean hydraulic depth for each passage will be substantially the same as that for any other passage. Fig. 8 shows in cross-section a modification of the heat-exchanging surfaces which will give the same mean hydraulic depth for each of the passages as the construction shown in Figs. 5 to 7. From the foregoing discussion of the invention and of the constructions for carrying out the novel process of the invention, it will be seen that the invention goes further than the conformance of the hydraulic mean depth with the total length of travel in a definite ratio of depth to length, even assuming that the depth has been chosen to give a desired high initial velocity which is substantially the extent of the prior art. 50

e spacing of the gas-confining and heatexchanging surfaces is varied from theirlower to their upper ends to maintain a velocity of fluid flow over the generating tubes which will produce suflicient turbulence at the reduced temperatures to give the desired degree of heat-transferring force. This results in a variation of the hydraulic mean depth. In this embodiment of the innot only is the hydraulic mean distribution of the heat transferring surface in the cross-sectional area of the passage at any point along its length is such that the cross-sectional area each-unit of surface is substantially identiof the gas stream j for cal with that for any other unit. In the the proper velocity relations. Moreover, an

approximation only to the most eflicient shaping of the respective passages is illus trated in the construction shown in Fig. 5 in order to permit showing the heat exchanging walls as straight division walls.

It will be understood that the invention is not necessarily restricted to an arrangement of the heat exchanging surfaces with their greatest linear dimensions extending alon the path of travel of the fluids but that other arrangements of these cluding the varying spacing thereof, may be made that will accomplish some or all of the objects of the invention.

This application is a division of my 'prioi' co-pending. application Serial No, 140,099, filed October 7, 1926 which has issued as Letters Patent No. 1,783,724, December 2, 1930.

We claim:

surfaces, in-

1. An apparatus for exchange of heat between fluids comprising a wall providing heat exchange surfaces on opposite sides thereof, means for causing one fluid to flow in contact with one surface and another fluid to flow in contact with the other surface, said parts being so arranged that the cross sectional area ofthe passage through which each fluid flows progressively decreases toward the zone of cooler temperature thereof. a

2. A heat exchanger for fluids comprising a plurality of walls all converging in the same direction to form tapered conduits through which the fluids flow in heat exchanging relation to said walls, the conduits being smaller in cross section ends thereof.

3. Apparatus for the exchange of heat between two fluids comprising walls forming at the cooler passages for the fluids extending in general converging in the same direction to form tapering conduits, means to cause the fluids to flow in a direction such that the cross sectional area of flow decreases toward the i ends at which the fluids are at lower temperature.

6. An apparatus for exchange of heat between fluids comprising walls forming co'ntional areas of which decrease progressively in said direction, means for introducing the hot fluid so as to flow in said direction through some of the conduits, and means for introducing the cooler fluid into the other conduits so as to flow on opposite sides of the walls to that on which the hotter fluid flows.

8. An apparatus for the exchange of heat between two fluids comprising walls defining a fluid passage which tapers from one end toward the other, a set of conduits in said passage which taper in the direction of the taper of the passage, said conduits being uniformly spaced from each other but more closely spaced at the smaller end of the passage than at the larger end thereof, and means for causing one fluid to flow through the passage and the second fluid to flow through the conduits.

9. An apparatus for transferring heat from a hotter to a cooler fluid comprisin means including dividing walls all converging in one direction and forming a set of passages which confine the flow of the hotter fluid for heat exchanging contact with said walls, said walls also forming a set of passages which confine the cooler, fluid so as to flow in the opposite direction \to the hotter fluid and in contact with said walls so as to receive the heat imparted thereto from the hotter fluid,

10. Heat exchange apparatus for two fluids comprising longitudinally extending walls converging towards one end and forming a plurality of adjacent conduits in heat exchange relation, all of which conduits taper gradually towards the said one end, means for introducing a heated fluid into the larger ends of a portion of the conduits and means for introducing acool fluid into the smaller ends of the other conduits in heat exchange relation therewith.

11. Heat exchange apparatus for two fluids comprising longitudinally extending Walls converging towards one end and forming a plurality of adjacent conduits in heat exchange relation, all of which conduits taper gradually towards the said one end, means for introducing a heated fluid into the larger ends of a portion of the conduits and means for introducing a cool fluid into the smaller ends of the other conduits in heat exchange relation therewith, said walls being so closely spaced that there is at least 

